The demand for precise detection of the position of incident light is crucial for a variety of applications, such as automatic focusing, position-sensing, movement monitoring, mirror alignment, distortion and vibration measurements, and for use within photocopy machines, facsimile machines, automatic lighting systems, articulated robotic beam delivery systems, optical switches and remote controls, optical range finders, laser displacement sensors, computer tomography and cameras. Each application requires an efficient and effective optoelectronic device to ascertain the correct coordinates.
Conventionally, various instruments, such as small discrete detector arrays or multi-element sensors, are used to detect the position of incident light. However, photodiode-based position-sensing detectors (PSDs) offer higher position resolution, higher speed response and greater reliability than other solutions. Photodiode-based PSDs convert an incident light spot into continuous position data and are manufactured from semiconductors such as silicon materials. Silicon photodiodes, essentially active solid-state semiconductor devices, are amongst the most popular photo detectors. In addition, silicon photodiodes detect the presence or absence of minute light intensities thereby facilitating correct measurement on appropriate calibration.
The abovementioned silicon photodiode have substantial disadvantages, however. Due to short cut-off wavelength of silicon materials, photodiodes manufactured from silicon are not suitable for applications that involve longer wavelengths such as in communication systems or eye safe detection applications. Therefore, PSDs employing materials other than silicon, such as indium-gallium-arsenide (InGaAs)/indium-phosphide (InP) which have a cut-off wavelength suitable for photo-detection, have been developed.
Conventionally, PSDs employing InGaAs/InP are classified as either one-dimensional or two-dimensional. Two-dimensional PSDs are more useful in ascertaining position than one-dimensional PSDs because they can detect movement in two dimensions and provide adequate details about coordinates. Two-dimensional PSDs are further divided into duo-lateral and tetra-lateral position sensing detectors.
Duo-lateral PSDs typically have two anode electrodes on the front side and two cathode electrodes on the backside. While duo-lateral PSDs have excellent position linearity, they tend to have relatively high dark current, low speed response and complicated application of reverse bias. Duo-lateral PSDs can be disadvantageous in that they are expensive to manufacture as they requires front-to-back mask alignment capability.
Accordingly, there is a need for a tetra-lateral PSD that can be manufactured at a lower cost than a duo-lateral PSD. In addition, there is a need for a tetra-lateral PSD InGaAs/InP photodiode that can be used in a longer wavelength region.